| A | B |
|---|
| hormone | One of many types of circulating chemical signals in all multicellular organisms that are formed in specialized cells, travel in body fluids, and coordinate the various parts of the organism by interacting with target cells |
| target cell | The portion of an organsim affected by a particular hormone |
| phototropism | Growth of a plant shoot toward or away from light |
| auxin | A class of plant hormones, including indoleacetic acid (IAA), having a variety of effects, such as phototropic response through the stimulation of cell elongation, stimulation of secondary growth, and the development of leaf traces and fruit |
| gravitropism | A response of a plant or animal in relation to gravity |
| lateral bud | Meristemic area on the side of a stem that gives rise to side branches |
| apical dominance | Concentration of growth at the tip of a plant shoot, where a terminal bud partially inhibits axillary bud growth |
| herbicide | A pesticide in which the active ingredient is a virus, fungus, bacteria, or a natural product derived from a plant source |
| cytokinin | A class of related plant hormones that retard aging and act in concert with auxins to stimulate cell division, influence the pathway of differentiation, and control apical dominance |
| gibberellin | A class of related plant hormones that stimulate growth in the stem and leaves, trigger the germination of seeds and breaking of bud dormancy, and stimulate fruit development with auxin |
| ethylene | The only gaseous plant hormone, responsible for fruit ripening, growth inhibition, leaf abscission, and aging |
| tropism | A growth response that results in the curvature of whole plant organs toward or away from stimuli due to differential rates of cell elongation |
| thigmotropism | The directional growth of a plant in relation to touch |
| short-day plant | A plant that flowers, usually in late summer, fall, or winter, only when the light period is shorter than a critical length |
| long-day plant | A plant that flowers, usually in late spring or early summer, only when the light period is longer than a critical length |
| photoperiodism | A physiological response to day length, such as flowering in plants |
| photochrome | Plant pigments that are responsible for photoperiodism |
| dormancy | A period during which growth ceases and metabolic activity is greatly reduced; dormancy is broken when certain requirements, for example, of temperature, moisture, or day length, are met |
| abscission layer | In plants, the dropping of leaves, flowers, fruits, or stems at the end of a growing season, as the result of formation of a two-layered zone of specialized cells (the abscission zone) and the action of a hormone (ethylene) |
| xerophyte | Plants that live in the desert biome |
| epiphyte | A plant that nourishes itself but grows on the surface of another plant for support, usually on the branches or trunks of tropical trees |
